Lewis Dot Structures: Neutral Compounds: Videos & Practice Problems

To draw the optimal Lewis dot structure for a molecule like formaldehyde (CH₂O), one must follow a systematic approach. Start by calculating the total valence electrons from the group numbers of the elements involved. Place the least electronegative element, excluding hydrogen and halogens, in the center and connect others with single bonds. Ensure surrounding elements have an octet of electrons, with the exception of hydrogen, which only requires two to resemble helium. If the central atom lacks an octet, introduce double or triple bonds as needed. Finally, assess the formal charges, aiming for the least number of charges, with negative charges on more electronegative elements, to ensure stability. For formaldehyde, the structure features carbon double-bonded to oxygen, with two hydrogens single-bonded to carbon, and oxygen having two lone pairs of electrons. This satisfies the octet rule for all atoms and results in no formal charges.

Lewis Dot Structures: Neutral Compounds

So realize when it comes to drawing Lewis dot structures that there are many possibilities that exist, but these are the rules that we're going to follow in order to draw the best structure. Now recall elements form bonds in order to gain electrons and become like the noble gases, the nearest noble gas. If we take a look here at this example question, it says draw the Lewis dot structure for formaldehyde molecule which is CH₂O.

All right, so in order to draw this let's look over the steps. So step one says we need to determine the total number of valence electrons of the structure. Recall valence electrons equal group number of the element. So here we have carbon which has four valence electrons +2 hydrogens. Each one has one itself. That's a total of 2 valence electrons. Oxygens in Group 6A, so it has six valence electrons. Adding all that up together gives us 12 total valence electrons.

Now Step 2, we're going to place the least electronegative element in the center and connect all elements with single bonds. All right. Now, there are exceptions to this exceptions. Hydrogen can never go in the center. Recall hydrogen only needs one more valence electron to adopt the same type of numbers of valence electrons as helium. So it does. It can't be in the center, it'd be overflowing with electrons. Also halogens. So remember the elements in groups 7A, Salt, fluorine, chlorine, bromine and iodine? They only make single bonds as a surrounding element.

All right, So what we're going to do here is we're going to put into practical We just set so we can't put hydrogen in the center. So our next best option is carbon. So carbon goes in the center and then we're going to place hydrogen and oxygen just to keep it like symmetrical. I put the hydrogens on the sides and the oxygen at the top. We said we're going to connect all of these elements with single bonds. So we're going to connect single, single and single.

Now add electrons to all surrounding elements until they have 8 electrons following the octet rule. So we want them to have 8 octet electrons around them. Exceptions. Hydrogens only want 2 octet electrons around them, because again, when they get to 2 octet electrons, they behave just like helium, their nearest noble gas. All right, so oxygen, we needed to have 8 octet electrons by following the octet rule. So right now we have these two electrons, so 3, 4, 5, 6, 7 and 8. And actually, let me bring that down so we get a better look at it.

So carbon goes here, and then we're connecting the hydrogens and we're connecting the oxygen. And then we have again these two electrons that are within this bond. Oxygen needs 8, so 3, 4, 5, 6, 7 and 8 right Now place any remaining electrons on the central element. So realize how many electrons have we used so far. We have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, so we have 12 electrons already used, so we don't have any additional electrons left to put around the carbon atom.

But this is what's important for Step 5. If any elements don't have 8 octet electrons, add double or triple bonds between them. If we look, carbon has 2, 4, 6 electrons around it. It needs two more to get to the octet rule. So what are we going to do? We're going to use one of these pair of electrons and bring it down and when we do that. So I'm going to take these pair of electrons and I'm going to bring them down and make a double bond with the carbon. So now we have a double bond with that carbon, and now carbon has a total of 8 electrons around itself. So what's following the octet rule? And the oxygen up above is also following the octet rule.

Now step 6. The formal charge can be used to determine if a Lewis dot structure is drawn correctly. The only allowable formal charges for an element are -1, zero, or +1. For stability, draw the structure that gives least formal least formal charges or lowest formal charges, and realize you're going to put the negative formal charge on the more electronegative element because that tends to be the most stable. In this case we don't have to do that because we see that the oxygen is following the octet rule by having 8 total octet electrons around it. Same with carbon. Hydrogen only makes single bonds, so we see that they're both making single bonds so we know they're satisfied as well.

So that means for the formaldehyde molecule we'd have hydrogen single bonded and then the oxygen and carbon would be double bonded to one another and then the oxygen would have these four non bonding electrons around itself. So this would be the best structure for formaldehyde.

Determine the Lewis Dot Structure for the disulfur dichloride molecule, S₂Cl₂.

• A.
• B.
• C.
• D.

Answer: (C)

Lewis Dot Structures: Neutral Compounds Example 1

So recall that nonbonding electrons are not involved in the bonds between elements and now a lone pair just represents a pair, so two of nonbonding electrons. If we look at this example, it says how many lone pairs does the sulfur atom possess in the hydrogen sulfide molecule.

We'd see here that sulfur has in total 4 non bonding electrons. And remember a lone pair is just a pair of those non bonding electrons. So here's a pair, and here's another pair. So sulfur would possess 2 lone pairs around it.

That mean that our answer would have to be option C.

How many lone pairs are on the central element for the following compound:AsH₃.

• A. 0
• B. 1
• C. 2
• D. 3

Answer: (B)

How many total bonding electrons are on the central element for the following compound:CO₂.

• A. 8 bonding electrons
• B. 6 bonding electrons
• C. 5 bonding electrons
• D. 3 bonding electrons

Answer: (A)

How many lone pairs are on the central element for the following compound:NOCl

• A. 0
• B. 1
• C. 2
• D. 3

Answer: (B)

Determine the Lewis Dot Structure for the silicon tetrabromide molecule, SiBr₄.

• A.
• B.
• C.
• D.

Answer: (A)

Determine the Lewis Dot Structure for the diazene molecule, N₂H₂.

Here it says to draw the Lewis dot structure for the diazine molecule. So here we're going to figure out how many valence electrons we have in total. Nitrogen is in group 5a, and there are 2 of them. Hydrogen is in group 1a and there are 2 of them. So it's going to be 10 + 2 which is 12. Hydrogen can't go in the center, so it's going to be the 2 nitrogens. Remember, hydrogens only make single bonds. So right now we've used a total of 2, 4, 6 electrons, meaning we have 6 electrons remaining. Alright. So then what do we do? We have 1, 2, 3, 4, 5, 6. We've used all of our electrons, but we have an issue. The nitrogen on the left has 8 electrons around it total, which is great, but then the one on the right doesn't. It has 2, 4, 6. Remember, if an atom is not following the octet rule and it needs to, we can make double or triple bonds. So that's what we're going to do. We're going to take one of these lone pairs and use it to make a triple bond. So here are our electrons that we had before, and I took one of the lone pairs here to make a double bond. In that way, both nitrogens are fulfilling the octet rule. Again, hydrogen only needs 2 electrons around it because it wants to resemble helium. So this would represent the correct Lewis dot structure of the diazine molecule.

Here’s what students ask on this topic:

How do you draw Lewis dot structures?

To draw Lewis dot structures, follow these steps:

1. Determine the total number of valence electrons: Add up the valence electrons from all atoms. For polyatomic ions, add an electron for each negative charge or subtract one for each positive charge.
2. Choose a central atom: Generally, the least electronegative atom that isn't hydrogen is placed in the center.
3. Sketch a skeleton structure: Connect the central atom to surrounding atoms with single bonds (lines), using a pair of electrons for each bond.
4. Distribute remaining electrons: Starting with the outer atoms, place the remaining electrons to satisfy the octet rule (8 electrons for most atoms, 2 for hydrogen).
5. Check and complete octets: Ensure each atom (except hydrogen) has an octet. If any atom lacks an octet, form double or triple bonds by sharing electrons between atoms.
6. For molecules with multiple valid structures (resonance): Draw all possible structures showing electron pair movement with double-headed arrows.

Remember, some molecules may not follow the octet rule, such as those with an odd number of electrons, or those with expanded octets (elements in period 3 or below can have more than 8 electrons).

What purpose do Lewis dot structures serve?

Lewis dot structures, also known as electron dot structures, are a visual representation of the valence electrons in an atom, ion, or molecule. These diagrams help in understanding the bonding between atoms and the arrangement of electrons. Each dot in the structure represents a valence electron, and each line represents a bond between two atoms. By arranging the dots around the elemental symbols, Lewis dot structures illustrate how atoms share or transfer electrons to achieve a full outer shell, which is the basis for the octet rule. This rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shell, giving them the same electronic configuration as a noble gas.

Lewis dot structures are particularly useful in predicting the number and types of bonds that can form, the arrangement of atoms within a molecule, and the presence of lone pairs of electrons that do not participate in bonding. This makes them an essential tool in understanding the chemical behavior and properties of elements and compounds.

What are Lewis dot structures?

Lewis dot structures, also known as Lewis diagrams, are a way to represent molecules that highlights the valence electrons of atoms. These diagrams are named after Gilbert N. Lewis, who introduced them in 1916. The valence electrons are the electrons in the outermost shell of an atom and are important in determining how atoms bond with each other.

In a Lewis dot structure, the element's symbol is used to represent the nucleus and inner electrons of the atom, while dots are placed around the symbol to denote the valence electrons. Single dots represent unpaired electrons, and pairs of dots represent paired electrons.

The arrangement of these dots around the atomic symbols helps illustrate the bonding in molecules. Single bonds are represented by a pair of dots (or a line) between two atoms, double bonds by two pairs (or two lines), and so on. These structures help predict the shape of molecules, the type of bonds between atoms, and the overall stability of the molecule. Understanding Lewis dot structures is fundamental in the study of chemistry, as they provide a visual way to grasp how atoms come together to form compounds.